The term "state dependent learning" (SDL) refers to a property of memory retrieval. Memories learned while an animal is in the drug state cannot be recalled when the animal is undrugged; however, the memories can be recalled whenever drug is present. The cause of SDL is unknown, although it occurs in rats, monkeys and humans. The present study attempts to identify the anatomical brain structures responsible for SDL. Individual brain structures will be stimulated electrically or chemically to induce an altered state, and the degree of resulting SDL will be evaluated in a two-bar operant discrimination task. Rats will be required to discriminate the presence vs. absence of various types of brain stimulation in this task. It is expected that stimulation of some brain structures will bery rapidly discriminated, by comparison with stimulation of most other structures. This will support the conclusion that SDL is primarily caused by drug-induced modification of the functions normally executed by these structures. Further investigations of the mechanism of SDL can focus on these structures.